BETA Can’t read the text? Switch theme 1. Python: Multiset Implementation A multiset is the same as a set except that an element might occur more than once in a multiset. Implement a multiset data structure in Python. Given a template for the Multiset class, implement 4 methods: • add(self, val): adds val to the multiset • remove(self, val): if val is in the multiset, removes val from the multiset; otherwise, do nothing •contains(self, val): returns True if val is in the multiset; otherwise, it returns False •len(self): returns the number of elements in the multiset Additional methods are allowed as
The Correct Answer and Explanation is:
Here is a correct implementation of the Multiset class in Python:
python
class Multiset:
def __init__(self):
self.elements = {}
def add(self, val):
if val in self.elements:
self.elements[val] += 1
else:
self.elements[val] = 1
def remove(self, val):
if val in self.elements:
self.elements[val] -= 1
if self.elements[val] == 0:
del self.elements[val]
def __contains__(self, val):
return val in self.elements
def __len__(self):
return sum(self.elements.values())
Explanation
A multiset is a collection that allows multiple instances of the same element. Unlike a typical set where each element must be unique, a multiset can contain duplicates. The implementation above captures this behavior using a dictionary named elements to store items as keys and their counts as values.
The constructor __init__ initializes the dictionary. When add(val) is called, the method checks whether the value already exists. If so, it increases the count. If not, it initializes the count to one. This ensures every added element is properly tracked by frequency.
The remove(val) method decreases the count of the given value only if it is present. If the value’s count drops to zero after removal, the method deletes it from the dictionary entirely. This prevents values with zero occurrences from lingering.
The method __contains__ enables the use of the in operator. It simply checks if the value exists in the dictionary, meaning it has at least one occurrence in the multiset.
The __len__ method calculates the total number of elements. It does not return the number of unique items, but rather the sum of all counts. For instance, if the multiset contains three “a”s and two “b”s, the length would be five.
This structure allows all operations to be handled efficiently. Looking up, adding, and removing elements can typically be performed in constant time due to the dictionary’s underlying hash table implementation. Additional methods such as listing elements or checking multiplicity can be added if further functionality is needed.
